Centrifugal separation of substances having different specific gravities is historical. Cyclone separators for removing sawdust from airstreams are an example of removal of solids from gases. Separation of solids from liquids is shown in Ford U.S. Pat. No. 5,811,006. In this patent the objective is to remove the “heavier” solids from a “lighter” liquid by centrifuging the solids-laden stream against the inner wall of a circular chamber, along which the heavier solid material flows to the bottom, while the liquid rises to and out of the top at the center of the swirling mass.
This concept has been extended to the separation of gases, both free and dissolved, from liquids. In this case, the heavier material is the liquid, and the lighter material is the gas. Examples are shown in Mazzei et at U.S. Pat. Nos. 5,338,341 and 5,622,545, and in Mazzei U.S. Pat. Nos. 5,674,312 and 6,193,893. It is this latter group of patents with which this invention is concerned. This invention is not concerned with elimination of solids from a liquid stream, but instead is concerned with removal of gases from a liquid stream.
The separation (extraction) of gases from liquids is a matter of great importance in many fields. It is particularly important when the gases to be separated are undesirable for several possible reasons. Such reasons might include their use and recovery as “sweeping” gases to carry with them some other existing gas of greater risk, or gases which involve their own problems such as corrosion or pollution.
Another, and rather surprising application is the separation of gases from liquid stream whose flow is to be measured. Water used in oil extraction systems is somewhat oily and frequently includes methane. The presence of the gas or gases frustrates the accurate measurement of the water flow. It is a useful function of this invention to remove the gases prior to measurement, thereby enabling accurate measurement. It is possible to return extracted gases to the liquid stream after measurement, which in some circumstances may be desirable.
While this invention will find its greatest employment separating gases from water with little or no saline content, it can be use to de-gas any liquid. Waters with considerable salinity, especially seawater are readily treated. The recovery of gases from such waters is otherwise usually quite difficult. therefore there is no limitation on the type of liquid. It merely must be amenable to rapid flow through the device.
In whatever event, the objective is to reduce as much as possible the presence of the gas in a liquid stream. The principal driving means is derived from the difference in the specific gravities of liquids and gases. The specific gravity of any liquid is far greater than that of any gas, so that centrifugal forces can separate gases from a liquid when in the free state.
There is another class of forces which are derived from pressure in the liquid. These are defined by Henry's Law, which relies on the difference between pressures perceived by the gas in the liquid and the gas phase contiguous to it. The lower pressures in the liquid caused by the rapid movement of the fluid through a reducing cross-section considerably reduce the solubility of the gases. This effect is of much less importance compared with the centrifugal forces, but is worth pursuing in some applications.
With special attention to U.S. Pat. Nos. 5,338,342 and 5,622,545, gases therein are separated through a central horizontally-slotted cylindrical tube located co-axially in a cylinder. One objective in patents is to contain in a quieter central region a quantity of water and gas, from which the gas rises and exits the system. This is a classical mass-separation technique, which only incidentally reduces the angular momentum of the liquid stream and does not optimally affect the pressure and velocity in the vortex chamber.
Such a usual centrifugal arrangement characterized by the above patents still involve a lively and undisciplined environment. If the objective is to rid the system of gas, a lively central region is not to be preferred. Instead, this invention proposes to combine an enhanced very forceful and lively centrifugal region of a liquid stream containing the gas, with an internal quiescent region where the separated gas can quietly rise from the system.
It is interesting to observe in a separator without a central tube, the conditions of the incoming stream, the whirling mix of liquid and gas as they begin to separate, and the lively vortex at the center, whose alignment, shape and length vary and move around, and is always rapidly rotating. Especially there is a rotation of the interface between water and the separating gases, this being the boundary of the vortex. It can readily be appreciated that the vortex itself and the gases in it are in vigorous motion.
In said U.S. Pat. Nos. 5,338,341 and 5,622,545 one of the inventors therein, and the sole inventor herein, attempted to stabilize the vortex by providing horizontal slots through the wall of a vertical cylinder located inside of a vertical, coaxial cylinder. The objective there was to limit the vortex to a defined region, and to a significant extent it did and does improve the separation of the gases from the water. However, it has not proved as effective as the instant invention, particularly in the removal of certain gases that are difficult to remove, for example radon. Also, its performance on seawater was less than optimal. The device of this function works well removing gases from seawater, which has always been regarded as a difficult task.
In this invention, the slots in the internal tube will not lie in planes normal to the axis of the tube, but rather at an angle to it, and thereby will provide a wall or walls that will be impinged upon by the fluids.
In addition, the forgoing earlier separator tended to require a considerable “foot print” in the sense of occupied real estate for its installation. The present device requires only a significantly smaller footprint, and is surprisingly small for the work that it does. In fact, one of its very useful embodiments is only about 15 inches tall and about 4.6 inches outer diameter and routinely treats a flow volume between about 5 and about 50 gallons per minute depending on the inlet and outlet pressures that are used.
While only purely cylindrical elements are shown in said patents, and they can be utilized in this invention, significant improvements have been obtained with the use of at least one tapered element (preferably both) which reduces the lateral dimension of the whirling stream as it flows to a lower outlet. This results in a faster linear speed, a greater centrifugal force, and a larger gradient for gas separation.